Halides diazonium salts

VINYL SUBSTITUTION WITH ORGANIC HALIDES, DIAZONIUM SALTS, ACID CHLORIDES, 842... 

Normally, the most practical vinyl substitutions are achieved by use of the oxidative additions of organic bromides, iodides, diazonium salts or triflates to palladium(0)-phosphine complexes in situ. The organic halide, diazonium salt or triflate, an alkene, a base to neutralize the acid formed and a catalytic amount of a palladium(II) salt, usually in conjunction with a triarylphosphine, are the usual reactants at about 25-100 C. This method is useful for reactions of aryl, heterocyclic and vinyl derviatives. Acid chlorides also react, usually yielding decarbonylated products, although there are a few exceptions. Likewise, arylsulfonyl chlorides lose sulfur dioxide and form arylated alkenes. Aryl chlorides have been reacted successfully in a few instances but only with the most reactive alkenes and usually under more vigorous conditions. Benzyl iodide, bromide and chloride will benzylate alkenes but other alkyl halides generally do not alkylate alkenes by this procedure. 

Now, let us take a simple functional group such as an OH and substitute it on our carbon atom. The carbinol we now have is capable of yielding only one C-C bond by way of substitution or one unsaturation on our carbon by means of elimination. Alcohols should then be classified under the FN = 1 group. Other oxygen based substituents such as ethers, carboxylic and sulfonic esters, and other heteroatom-containing derivatives such as amines and sulfides behave similarly, as long as we have only one of the heteroatoms substituted on our central carbon. By the same token, alkyl halides, diazonium salts, and even the carbenium ion itself are all capable of giving only one C-C bond with carbon... 

Ketene aminals can be transformed by various electrophilic reagents to amidinium salts, thus mineral acids, alkyl halides, A///-dialkyliminium salts, alkoxymethyleneiminium salts, formamidinium salts, acyl halides, diazonium salts, vinylogous amidinium salts,sulfonyl halides, ketene dichlorides ... 

F. Alonso, Y. MogUe, G. Radivoy, M. Yus, Click chemistry from organic halides, diazonium salts and anilines in water catalyzed by copper nanoparticles on activated carbon, Org. Biomol. Chem. 9 (2011) 6385-6395. 

Gattermann s reaction A variation of the Sandmeyer reaction copper powder and hydrogen halide are allowed to react with the diazonium salt solution and halogen is introduced into the aromatic nucleus in place of an amino group. 

Gattermann (1890) found that the preparation of the cuprous halide may be avoided by making use of the fact that finely-divided copper (e.g., freshly-precipitated or reduced by hydrogen or copper bronze) acts catal3d.ically in the decomposition of solutions of diazonium salts, for example ... 

The diazonium salts 145 are another source of arylpalladium com-plexes[114]. They are the most reactive source of arylpalladium species and the reaction can be carried out at room temperature. In addition, they can be used for alkene insertion in the absence of a phosphine ligand using Pd2(dba)3 as a catalyst. This reaction consists of the indirect substitution reaction of an aromatic nitro group with an alkene. The use of diazonium salts is more convenient and synthetically useful than the use of aryl halides, because many aryl halides are prepared from diazonium salts. Diazotization of the aniline derivative 146 in aqueous solution and subsequent insertion of acrylate catalyzed by Pd(OAc)2 by the addition of MeOH are carried out as a one-pot reaction, affording the cinnamate 147 in good yield[115]. The A-nitroso-jV-arylacetamide 148 is prepared from acetanilides and used as another precursor of arylpalladium intermediate. It is more reactive than aryl iodides and bromides and reacts with alkenes at 40 °C without addition of a phosphine ligandfl 16]. 

The two main methods for the preparation of ar-yl halides, halogenation of arenes by electrophilic aromatic substitution and preparation by way of ar-yl diazonium salts, were described earlier and are reviewed in Table 23.2. A number of ar-yl halides occur naturally, some of which are shown in Figure 23.1. 

For aryl halides and sulfonates, even active ones, a unimolecular SnI mechanism (lUPAC Dn+An) is very rare it has only been observed for aryl triflates in which both ortho positions contain bulky groups (fe/T-butyl or SiRs). It is in reactions with diazonium salts that this mechanism is important ... 

One of the best methods for the introduction of iodine into aromatic rings is the reaction of diazonium salts with iodide ions. Analogous reactions with chloride, bromide, and fluoride ions give poorer results, and 14-25 and 13-20 are preferred for the preparation of aryl chlorides, bromides, and fluorides. However, when other diazonium reactions are carried out in the presence of these ions, halides are usually side products. Aniline has also been converted to fluorobenzene by treatment with t-BuONO and Sip4 followed by heating. A related reaction between PhN=N—N C4Hg and iodine gave iodobenzene. ... 

Reaction of aryl organometallic compounds with halogens Aryl halide exchange halo-denitration halo-dehydroxylation Reaction between diazonium salts and iodide ion Heating of diazonium fluoroborates (Schiemann)... 

Examples of the three mechanistic types are, respectively (a) hydrolysis of diazonium salts to phenols89 (b) reaction with azide ion to form aryl azides90 and (c) reaction with cuprous halides to form aryl chlorides or bromides.91 In the paragraphs that follow, these and other synthetically useful reactions of diazonium intermediates are considered. The reactions are organized on the basis of the group that is introduced, rather than on the mechanism involved. It will be seen that the reactions that are discussed fall into one of the three general mechanistic types. 

Aryl Halides from Diazonium Ion Intermediates. Replacement of diazonium groups by halides is a valuable alternative to direct halogenation for the preparation of aryl halides. Aryl bromides and chlorides are usually prepared by a reaction using the appropriate Cu(I) salt, which is known as the Sandmeyer reaction. Under the classic conditions, the diazonium salt is added to a hot acidic solution of the cuprous halide.99 The Sandmeyer reaction occurs by an oxidative addition reaction of the diazonium ion with Cu(I) and halide transfer from a Cu(III) intermediate. 

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